Embodiments of the present invention are directed generally to cable network fault identification and isolation and more specifically to the identification and isolation in components of a hybrid fiber coax (HFC) cable network that support two-way connectivity between subscribers and a headend.
Cable networks deliver voice, data, and video to subscribers over a complex network of headends, regional data centers, hubs, and nodes. At the upstream terminus of the network is the headend and regional data center. Typically, a head end comprises the analog and digital video signal processors, video on demand systems, and other video content management devices. A regional data center comprises digital service management devices (e-mail servers, DNS, and Internet connectivity) and routers that interconnect the regional data center with a headend. A hub receives the video and data signals from the headend and regional data center, processes these signals through appropriate modulators, and sends these signals downstream to a hub. The hub provides the signals to a node that is ultimately associated with individual subscribers. A node provides an interface between the fiber-based component of the HFC cable network and the RF/cable component of the network that is the transport media to the home.
In a commercial network, a headend may service multiple hubs and a hub may service multiple nodes. A regional data center may provide digital services to multiple headends. From a node to the home, the RF/cable component of the HFC cable network may branch numerous times. Amplifiers, line extenders, and passive devices are employed to maintain signal quality across all branches (or “cascades”) serviced by the node.
FIG. 1 illustrates typical prior art cable system architecture. A headend 100 comprises a network control system 102 that handles set-top provisioning, system management and interactive session set-up, a video signal processor 104 that handles content acquisition and delivery, 256 QAM Modulators 111 that generate modulated RF streams of digital video signals, a high-speed data interface 106, and a billing system 107.
Headend 100 communicates with hub 108. Hub 108 comprises a cable modem termination system 110, a 256 QAM modulator 112 for downstream data traffic, a QPSK modulator for downstream Out-of-Band Data traffic 114, and a QPSK demodulator 116 for upstream Out-of-Band Data traffic. As will be appreciated by those skilled in the art, a hub may comprise multiple instances of each device illustrated in FIG. 1.
Hub 108 communicates with nodes 120A, 120B and 120C. Nodes 120 provide an interface between the fiber-based transport medium of the cable network (between the headend 100 and upstream side of nodes 110) and the coax-based medium (between the downstream side of nodes 110 and the subscriber interface 145). The downstream side of node 110B is further illustrated as connecting to bridger amplifier 1 125 which in turn is connected to bridger amplifier 2 130. The serial path from node 120B through bridger amplifier 1 125 to bridger amplifier 2 130 is referred to as a cascade relative to node 120B. Bridger amplifier 1 125 has three branches that are cascades relative to bridger amplifier 1 125 and sub-cascades relative to node 120B.
As will be appreciated by those skilled in the art, FIG. 1 is a greatly simplified schematic of cable network architecture. A hub typically serves 20,000 subscribers. A typical hub supports from 50 to 100 nodes with each node capable of serving 250 to 2000 subscribers. In order to maintain signal quality and quality of service commitments, trunk amplifiers maintain high signal quality. Internal bridger modules in the trunk amplifiers boost signals for delivery to subscribers' homes. Line Extender amplifiers maintain the high signal levels in cascade after the trunk amplifiers, through the neighborhoods. Taps divide out small amounts of signal for connection to the homes. Nominal cascade limits are up to 4 trunk amplifiers followed by up to 3 line extenders, with more in very rural areas. In suburban areas, cascades typically comprise 2 trunk and 2 line extenders. Because branching is unlimited, the total device count per node may be large despite short cascades.
At the downstream end of the network is the customer premises equipment (CPE). Referring again to FIG. 1, subscriber interface 145 connects a set top box (STB) 150 and a cable modem (CM) 155 to the HFC cable network. The CPE receives content from a headend or regional data center and provides access to it by a subscriber. For example, video programming is delivered to STB 150 and high-speed data services are delivered to CM 155.
The complexity of cable networks makes network fault isolation and maintenance a challenging task. The task can be partitioned into four stages:                determining that a failure has occurred;        determining what has failed;        determining where in the network the failure is likely to be; and        determining that a network is imminently approaching failure.        
A failure in any of the system components that provide services will ultimately cause subscribers to complain. However, relying on subscriber complaints to identify network faults is not only bad for business but, in many situations, too imprecise to be helpful. Further, customer complaints represent the existence of a problem rather than forecast that a problem is developing. Reliance on such data alone for network fault isolation and maintenance precludes proactive responses by the cable operator. While network-wide fault identification systems may ultimately identify the existence of a fault and its location, such systems typically work with large volumes of data that is evaluated over time. Hence, they do not provide a real time measure of the health of the two-way components of an HFC cable network.
What would be useful is a system and method that alerts a cable operator of the occurrence of a fault within critical components of a HFC cable network in “real-time” and facilitates the isolation of the cause of the fault.